It is well known in the processing industries to treat liquid and gaseous substances by contacting them with solids such as granular agents. Such processes are often called "sorption" processes and are usually performed in beds which include a tank or vessel with a supporting grid or screen onto which a layer of granular agent is evenly distributed and through which layer the liquid or gaseous substance flows and is subjected to the sorption treatment. In this respect, the screen has a mesh size small enough to avoid entrainment of the granular agent.
Inherent disadvantages of the above-described beds are that they require renewal of the granular agent after exhaustion of its activity; and, this, in turn, requires a means to drain the granular agent and a means to refill the bed with fresh agent. Additionally, the layer of granular agent has to be of an even thickness to obtain a constant contact-time of the liquid or gaseous substance as it flows in a perpendicular direction through the whole layer-area of the granular agent.
Other known contact assemblies for sorption processes include those where a granular agent is located between two screens which are arranged such that the granular layer can be oriented in any desired angle such as vertically, for example. In this manner, with a vertically oriented layer, the direction of flow of the liquid or gaseous substance can be horizontal. An assembly of this type, however, has the disadvantage that, during its use, the granular agent tends to settle thereby leaving a space for a reduced-density portion at the upper edge of the layer. In such event, portions of the liquid or gaseous substance can flow through the assembly while having little or no contact with the granular agent. Some of the substance, therefore, remains untreated or poorly treated because of the reduced contact-time with the granular sorption agent. This disadvantage has been overcome in the past by using flexible, but tight, membranes pressed onto the upper edges of the assembly by springs or the like, but these are costly and not always desirable.
Fibrous mats have also been used to support granular agents. Such mats, however, have been impregnated with a powdered agent that is retained by means of a sticky or gluey coating applied to the fibers. This has the serious disadvantage of reducing the contact-area of the agent wherever the agent is covered by the sticky or gluey coating.
It is an object of this invention, therefore, to provide a mechanically stable mat containing at least one layer of granular sorption agent which is easily replaced; and, wherein a liquid or gaseous substance flowing across the granular agent is subjected to a uniform contact-time with the granular agent.